The metabolism of fatty acids in human Bietti crystalline dystrophy

PURPOSE

To investigate the role of abnormal lipid metabolism in Bietti crystalline dystrophy.

METHODS

Cultured human lymphocytes and fibroblasts from patients with Bietti crystalline dystrophy (BCD) were incubated in the presence of [(14)C]18:3n-3 or [(14)C]18:2n-6. Incorporation into the cellular lipid pools and further metabolism by desaturation or elongation were monitored by thin-layer chromatography and HPLC. Results were compared with those in normal control subjects and patients with Wolman disease (WD).

RESULTS

Pulse-chase experiments with labeled fatty acids in all groups showed that, after 1 hour, radioactivity was largely confined to the triacylglyceride (TG) and choline phosphoglyceride (CPG) pools. However, after several hours, radioactivity was transferred from the TG and CPG pools, some going to the serine and ethanolamine phosphoglyceride (SPG and EPG) pools. Fibroblasts from all groups showed direct transfer of fatty acids (FAs) into CPG and EPG. Incorporation of labeled FAs into the EPG pool paralleled extensive desaturation and elongation of 18:2n-6 to 22:5n-6 and 18:3n-3 to 22:6n-3. Fibroblasts from patients with WD (a lysosomal acid lipase deficiency characterized by excessive lipid accumulation), showed higher incorporation of 18:2n-6 into TGs than did normal or BCD fibroblasts. Conversely, fibroblasts from patients with BCD showed lower conversion of 18:3n-3, but not of 18:2n-6, into polyunsaturated FAs (PUFAs) than those of normal subjects or patients with WD. This was true for total FAs, CPGs, and EPGs. Similar results were found in both fibroblasts and lymphocytes; however, unlike fibroblasts, lymphocytes from normal subjects showed similar levels of incorporation of FAs into EPGs and CPGs. In contrast, incorporation of 18:3n-3 into EPGs was decreased in lymphocytes from patients with BCD.

CONCLUSIONS

BCD is characterized by a lower than normal conversion of FA precursors into n-3 PUFA, whereas there is a higher than normal level of n-6 and n-3 FAs incorporation into TGs in cells from patients with WD. These findings raise the possibility that abnormal lipid metabolism associated with BCD is the result of deficient lipid binding, elongation, or desaturation in contrast to the lysosomal acid lipase deficiency found in Wolman disease.

Oxidative stress induces heme oxygenase-1 immunoreactivity in Müller cells of mouse retina in organ culture

PURPOSE

Heme oxygenase (HO)-1 immunoreactivity (IR) was examined in normal untreated retina and in retinal explants after in vitro treatment with stress agents.

METHODS

Enucleated eyes from young adult C3H mice were immediately fixed and cryosectioned and the retina sections processed for immunocytochemistry with antibodies against HO-1 and glial fibrillary acidic protein (GFAP). From other eyes retinas were isolated and maintained in organ culture, either untreated for 4 days maximum or for 21 hours during which the explants were treated the first 3 hours with selected doses of sodium arsenate or hydrogen peroxide. Thereafter, the explants were processed identically with the normal tissue.

RESULTS

In the normal retina, HO-1 and GFAP IR was very low. The culturing itself resulted in an increase in both HO-1 and GFAP immunolabeling in Müller cells of explanted retinas. Both sodium arsenate and hydrogen peroxide further induced strong HO-1 IR in Müller cells but not in other retinal cells. In contrast to HO-1, GFAP staining in Müller cells was not altered as a result of treatment, either by sodium arsenate or hydrogen peroxide at any concentration used.

CONCLUSIONS

The results show for the first time that HO-1 can be induced in the retina in vitro by conditions of oxidative stress and that enzyme expression is confined exclusively to Müller cells.

Clusterin protein diversity in the primate eye

PURPOSE

The clusterin gene encodes a multi-functional protein that has been identified in different tissues, including a number of different eye tissues, primarily in the mouse and to a much lesser extent in humans. Clusterin has been implicated in a number of cellular processes such as lipid transport, membrane integrity, apoptosis, and neurodegeneration, all of which could be important to the biology of the eye. In the current communication, we provide data that confirms the expression of clusterin in a number of different human eye tissues and establishes the expression profile of this gene in monkey derived eye tissues. The issue that we sought to examine is whether a broad profile of clusterin expression in the eye is consistent in primates (monkey and human).

METHODS

The majority of our study was done using monkey eye tissues. Where possible, we have used human tissues in order to confirm published findings. Northern and western analysis was performed using tissues derived from monkey eyes. In situ hybridization and immunochemistry were carried out on human eye sections.

RESULTS

Clusterin mRNA is expressed in primate lens, cornea, limbus, sclera, orbital muscle, ciliary body, retina, RPE/choroid, and RPE cells in culture. Western analysis revealed that two major groups of clusterin exist in the eye, a high molecular weight group (>100 kDa) and a second group consisting of at least five clusterin species that are all approximately 80 kDa. Analysis of conditioned media from RPE cells cultured on permeable supports suggests that different forms of clusterin display alternative patterns of secretion.

CONCLUSIONS

Clusterin is expressed in a broad range of eye tissues in both human and monkey, suggesting that this is a characteristic feature in primates. We demonstrate for the first time that a diverse number of clusterin isoforms were observed in monkey eye tissues by western analysis. Meanwhile, the molecular size of clusterin mRNA detected in the array of tissues are identical in size, suggesting that the nature of the diversity in clusterin forms is due to post-translational modifications. In addition, new insights were made in defining clusterin expression in ciliary body, cornea, and the retinal pigment epithelium.

Recombinant forms of the neurotrophic factor pigment epithelium-derived factor activate cellular metabolism and inhibit proliferation of the RAW macrophage cell line

Recombinant forms of the neurotrophic factor pigment epithelium-derived factor (PEDF) activate metabolism of RAW macrophage cells while simultaneously inhibiting their proliferation. The recombinant forms (rPEDF) acted with EC(50)s of 0.1-1 nM while full-length native bovine PEDF was inactive. Urea, which is the buffer used to extract recombinant PEDF, stimulated RAW cell proliferation, the first report of an effect of urea on non-kidney cells. PEDF acted within 12 h and its effects persisted up to 72 h with continuous exposure. Although rPEDF had no direct action on glioma cell lines, it increased the amount of a soluble factor released by RAW cells which was capable of blocking glioma cell division. Thus PEDF may function as a neuroimmune modulator, affecting both neural and immune system cells.

Identification, isolation, and characterization of a 32-kDa fatty acid-binding protein missing from lymphocytes in humans with Bietti crystalline dystrophy (BCD)

Bietti crystalline dystrophy (BCD) is an autosomal recessive retinal degeneration characterized by intraretinal lipid inclusions with degeneration of the retina and sclerosis of the choroidal vessels, resulting clinically in progressive night blindness and constriction of the visual fields. Characterization of fatty acid metabolism in Bietti crystalline dystrophy suggested that BCD might result from abnormalities in lipid-binding proteins or one or more enzymes active in fatty acid elongation and desaturation. To further investigate the first possibility, the docosahexaenoic acid-binding proteins (DHABPs) of human lymphocytes from patients with Bietti crystalline dystrophy were studied and compared with those of normal controls. For fatty acid-binding protein (FABP) identification, lymphocyte cytosol was first subjected to Lipidex 1000 chromatography. FABPs were then cross-linked with [14C]22:6n-3 and identified by HPLC and SDS-PAGE. Ten major peaks corresponding to calculated molecular weights of 13, 14, 32, 43, 45, 50, 64, 96, 105, and 186 kDa exhibit high-affinity binding of fatty acids. Significantly, peaks corresponding to two fatty acid-binding proteins of 32 and 45 kDa present in age-matched controls are absent from lymphocytes of patients with BCD. The 32-kDa fatty acid-binding protein present in normal individuals but absent from patients with BCD was isolated from cultured control human lymphocytes, its fatty acid-binding properties were characterized, and its amino acid composition was analyzed. It shows specific binding of 3n-3 fatty acids, consistent with the pattern of abnormalities of lipid metabolism demonstrated in patients with BCD. These results suggest that the 32- and 43-kDa FABPs are reasonable candidates for causing BCD.

Pigment epithelium-derived factor (PEDF) differentially protects immature but not mature cerebellar granule cells against apoptotic cell death

We have shown previously that pigment epithelium-derived factor (PEDF) acts as a survival factor for cerebellar granule cell neurons in culture, as well as protecting them against glutamate toxicity. In this study we have examined effects of PEDF on apoptotic cell death. We find that the granule cells die of apoptosis throughout the culture period, what we have termed "natural" apoptosis. PEDF prevents this natural apoptosis if added to immature cells, within the first 2 days in vitro (DIV), and the effect is maintained for up to DIV12. However, PEDF has no effect if added to mature cells at DIV5. Similar results are obtained when apoptosis is induced by shifting the cells from a serum- and 25 mM KCl-containing medium to serum-free medium with 5 mM KCl. PEDF most effectively blocks induced apoptosis in immature cells (DIV2) when added 24 hr prior to the change of medium, but still provides some protection when added simultaneously. However, 24 hr pretreatment with PEDF has a minimal effect when apoptosis is induced in mature DIV6 cells; addition at the same time is completely ineffective. Two polypeptide fragments of PEDF, only one of which contains the serine-protease inhibitory site, are equally active, supporting previous results which suggest that the neurotrophic effects of PEDF are not mediated by protease inhibition. We conclude that PEDF protects immature but not mature granule cells against both natural and induced apoptosis.

Structural and comparative analysis of the mouse gene for pigment epithelium-derived factor (PEDF)

PURPOSE

Pigment epithelium-derived factor (PEDF), a neurotrophic protein, is a member of the serine protease inhibitor supergene family. PEDF promotes both neuronal phenotype in cultured Y79 cells and neuronal survival in cultured cerebellar granulocytes. The purpose of this study was to clone the mouse PEDF gene and to determine its structure and levels of expression in different tissues.

METHODS

The mouse PEDF cDNA was cloned from a mouse liver cDNA library using human PEDF cDNA as a probe. The mouse PEDF gene was cloned from a mouse ES genomic P1 library. DNA sequencing was performed using a PE-Applied Biosystems model 373 automated fluorescent sequencer.

RESULTS

The mouse PEDF cDNA is 1461 bp in length and contains an open reading frame of 417 amino acids. The mouse PEDF gene spans approximately 13 kb and, like the human, it is fragmented into 8 exons. The splice sites follow the AG/GT consensus rule. Southern blot analysis indicates that the mouse genome contains only one gene for PEDF. Northern blot analysis shows the presence of the PEDF transcript in a broad range of adult mouse tissues with liver showing the highest level of expression.

CONCLUSIONS

The mouse and human PEDF promoters share overall 27% similarity but are nearly identical between mouse +86 to -166 and human +102 to -96. The present study will allow us to move from in vitro experiments to in vivo studies through the development of a "knock-out" mouse model.

Pigment epithelium-derived factor (PEDF) has direct effects on the metabolism and proliferation of microglia and indirect effects on astrocytes

Pigment epithelium-derived factor (PEDF), a neurotrophic agent first identified in conditioned medium from cultured human retinal pigment epithelial cells, induces neuronal differentiation with neurite outgrowth in Y-79 retinoblastoma cells and has a neurotrophic survival effect on cerebellar granule cells in culture. In the present study, we investigated the effects of human recombinant PEDF (rPEDF) on proliferation and activation of microglia and astrocytes isolated from newborn rat brain. rPEDF treatment caused microglia to round up morphologically, increased their metabolic activity (measured by both MTS conversion and acid phosphatase activity), but blocked proliferation (mitosis). This blocking effect could be demonstrated in cultures stimulated to proliferate by addition of granulocyte-macrophage colony stimulating factor. The effect of rPEDF on microglial metabolic activity showed a dose-response relationship both in serum-containing medium and in chemically defined medium and was blocked with anti-PEDF antibody. rPEDF had no direct effect on the metabolic activity or proliferation of cultured astrocytes but blocked their proliferation in astrocyte-microglia co-cultures. Proliferation of isolated astrocytes was also blocked by conditioned medium from microglia treated with PEDF (PMCM). The effect of PMCM on astrocytes was not blocked by an antibody to transforming growth factor-beta. These results demonstrate that PEDF activates microglial metabolism while blocking proliferation and suggest that a soluble factor(s) released by rPEDF-stimulated microglia blocks the proliferation of astrocytes. Thus, PEDF could play an important role in regulation of glial function and proliferation in the central nervous system.

Mutation analysis and loss of heterozygosity of PEDF in central nervous system primitive neuroectodermal tumors

Deletion of 17p is the most frequent abnormality observed in central nervous system (CNS) primitive neuroectodermal tumors (PNETs), implicating the presence of a tumor suppressor gene which maps to 17p. The gene for pigment epithelium-derived factor (PEDF) has been cloned and mapped to 17p13. PEDF belongs to the serine protease inhibitor (SERPIN) gene family. The PEDF protein has neurotrophic and neuronal-survival activities and is expressed in the CNS. Twenty tumor and matched normal DNA samples from patients with PNETs were screened by single-strand conformation polymorphism (SSCP) analysis to determine loss of heterozygosity (LOH) and to identify potential mutations within the 8 exons of the PEDF gene. Ten of the 20 tumors demonstrated LOH, consistent with the deletion status of 17p determined by cytogenetic or fluorescence in situ hybridization studies. SSCP analysis of the genomic DNA from the 10 cases with LOH demonstrated several polymorphisms in exons 4 and 7, but no mutations. Our results are consistent with a loss of alleles on 17p in 50% of CNS PNETs, but do not suggest that PEDF is a candidate for the PNET suppressor gene in 17p13.

Human gene for the RNA polymerase II seventh subunit (hsRPB7): structure, expression and chromosomal localization

The human gene for the seventh largest subunit of RNA polymerase II complex, hsRPB7 was cloned, sequenced and mapped. This complex is an integral part of the transcription-coupled DNA repair mechanism and has been shown to be involved in several human genetic diseases and implicated in many others. The hsRPB7 gene consists of 8 exons and spans approximately 5.1 kb. Southern blots of genomic and cloned DNA suggest that hsRPB7 is coded for by a single gene. Using human radiation hybrids and YACs, the gene was localized to 11q13.1, within 70 kb of marker D11S1765. The sequence of the 5' flanking region does not contain a TATA element, but does contain several Sp1 binding sites, an AP-1 site and a novel inverted polymorphic GATA tandem repeat. This novel GATA repeat can be used for linkage analysis. The hsRPB7 gene seems to be highly conserved among eukaryotic species, showing general sequence conservation to yeast and Drosophila. Northern blot analysis reveals a high degree of tissue-specific expression. For example, adult retina, brain and kidney exhibit a relatively high level of expression. A moderate level of expression is observed in heart, lung, testis, cornea, retinal pigmented epithelium/choroid and placenta with a lower level of expression in the uterus, small intestine and skeletal muscle. A very low level of expression was observed in stomach and liver. Comparison between four fetal and adult tissues also demonstrate a surprising level of developmental specificity. Expression in fetal retina is considerably lower than fetal brain but similar to adult retina.

Identification of components of a phosphoinositide signaling pathway in retinal rod outer segments

Phototransduction in retinal rods involves a G protein-coupled signaling cascade that leads to cGMP hydrolysis and the closure of cGMP-gated cation channels that are open in darkness, producing a membrane hyperpolarization as the light response. For many years there have also been reports of the presence of a phosphoinositide pathway in the rod outer segment, though its functions and the molecular identities of its components are still unclear. Using immunocytochemistry with antibodies against various phosphoinositide-specific phospholipase C (PLC) isozymes (beta1-4, gamma1-2, and delta1-2), we have found PLCbeta4-like immunoreactivity in rod outer segments. Similar experiments with antibodies against the alpha-subunits of the G(q) family of G proteins, which are known to activate PLCbeta4, have also demonstrated G(alpha11)-like immunoreactivity in this location. Immunoblots of total proteins from whole retina or partially purified rod outer segments with anti-PLCbeta4 and anti-G(alpha11) antibodies gave, respectively, a single protein band of the expected molecular mass, suggesting specific labelings. The retinal locations of the two proteins were also supported by in situ hybridization experiments on mouse retina with probes specific for the corresponding mouse genes. These two proteins, or immunologically identical isoforms, therefore likely mediate the phosphoinositide signaling pathway in the rod outer segment. At present, G(alpha11) or a G(alpha11)-like protein represents the only G protein besides transducin (which mediates phototransduction) identified so far in the rod outer segment. Although absent in the outer segment layer, other PLC isoforms as well as G(alpha q) (another G(q) family member), are present elsewhere in the retina.

Pigment epithelium-derived factor protects cultured cerebellar granule cells against glutamate-induced neurotoxicity

Pigment epithelium-derived factor (PEDF) is a survival factor for cerebellar granule cells in culture. In the present study, we have investigated the ability of a recombinant form of PEDF (rPEDF) to protect against glutamate neurotoxicity. When rPEDF was added to cerebellar granule cell cultures 30 min before addition of 100 microM glutamate, glutamate-induced neuronal death was significantly reduced. The protective effect of rPEDF was dose-dependent in the range from 0.023 to 7.0 nM (1-500 ng/ml), with a half-maximal dose of 0.47 nM. An antibody to rPEDF blocked this protective effect. Measurement of intraneuronal free calcium levels demonstrated that rPEDF raised the basal calcium content. However, after the elevation of intracellular calcium in response to administration of glutamate, rPEDF reduced the plateau level seen in the presence of glutamate. These data show that PEDF can protect neurons against glutamate-induced neurotoxicity, possibly via a calcium-related pathway. The finding that only 30 min of preincubation is required for the neuroprotective effect, significantly faster than other known neurotrophic factors, suggests that PEDF may be useful clinically as a neuroprotective agent in the CNS.

Organization, evolutionary conservation, expression and unusual Alu density of the human gene for pigment epithelium-derived factor, a unique neurotrophic serpin

PEDF is a neurotrophic serpin that promotes a neuronal phenotype and augments neuronal cell survival. The isolation, sequence and structural analysis of the human PEDF gene and its promoter along with its evolutionary conservation and expression in human tissues are now described. The gene spans approximately 16 kb and is divided among 8 exons and 7 introns, the junctions of which conform to the AG/GT consensus rule. PEDF appears to fall into the ovalbumin/PAI-2 subgrouping of serpins and is structurally far different from GDN/PN-1, the only other neurotrophic serpin reported to date. The immediate 5'-flanking region is dominated by a dense cluster of Alu repeats in which are embedded several promoter consensus sequences. A CAAT box is present at -43. The putative promoter region is also far different from that reported for GDN/PN-1. Comparable hybridization signals of 23 kb EcoRI fragments containing the PEDF gene are observed by Southern blot analysis in all primate, mammal and avian species examined; conservation is particularly evident among the primates. Northern blot analysis confirms the presence of the PEDF transcript in a broad range of human fetal and adult tissues including almost all brain areas examined, underscoring differences with GDN/PN-1 which, in the adult brain, is only expressed in glia and a subset of neurons.

Scleral matrix metalloproteinases, serine proteinase activity and hydrational capacity are increased in myopia induced by retinal image degradation

In the avian model of myopia, retinal image degradation quickly leads to ocular enlargement. We now give evidence that regionally specific changes in ocular size are correlated with both biomechanical indices of scleral remodeling, e.g. hydration capacity and with biochemical changes in proteinase activities. The latter include a 72 kDa matrix metalloproteinase (putatively MMP-2), other gelatin-binding MMPs, an acid pH MMP and a serine protease. Specifically, we have found that increases in scleral hydrational capacity parallel increases in collagen degrading activities. Gelatin zymography reveals that eyes with 7 days of retinal image degradation have elevated levels (1.4-fold) of gelatinolytic activities at 72 and 67 kDa M(r) in equatorial and posterior pole regions of the sclera while, after 14 days of treatment, increases are no longer apparent. Lower M(r) zymographic activities at 50, 46 and 37 kDa M(r) are collectively increased in eyes treated for both 7 and 14 days (1.4- and 2.4-fold respectively) in the equator and posterior pole areas of enlarging eyes. Western blot analyses of scleral extracts with an antibody to human MMP-2 reveals immunoreactive bands at 65, 30 and 25 kDa. Zymograms incubated under slightly acidic conditions reveal that, in enlarging eyes, MMP activities at 25 and 28 kDa M(r) are increased in scleral equator and posterior pole (1.6- and 4.5-fold respectively). A TIMP-like protein is also identified in sclera and cornea by Western blot analysis. Finally, retinal-image degradation also increases (approximately 2.6-fold) the activity of a 23.5 kDa serine proteinase in limbus, equator and posterior pole-sclera that is inhibited by aprotinin and soybean trypsin inhibitor. Taken together, these results indicate that eye growth induced by retinal-image degradation involves increases in the activities of multiple scleral proteinases that could modify the biomechanical properties of scleral structural components and contribute to tissue remodeling and growth.

Structural organization and chromosomal localization of the human ribosomal protein L9 gene

The intron-containing gene for the human ribosomal protein L9 has been cloned, sequenced and localized. The gene is approximately 5.5 kb in length and contains 8 exons. Splice sites follow the AG/GT consensus rule. The message for human rpL9 is 712 nt in length and is detected in all tissues examined. In the adult, expression is highest in retina and liver while brain shows highest expression among the fetal tissues tested. The transcription start site contains an oligopyrimidine tract, TTCTTTCTT, similar to those found in other ribosomal protein genes. As in other previously characterized ribosomal protein genes, a TATA box is absent from the 5' flanking region but a number of elements recognized by common transcription factors are present including Sp1 sites, CACCC boxes, inverted CCAAT boxes, and GATA elements. Another possible element of interest in the rpL9 5' flanking region is RFX1 also found in the well characterized rat rpL30 promoter. The gene was mapped by fluorescent in situ hybridization to band 13p of chromosome 4. At least 8 possible pseudogenes are present in the human genome, one of which is on Xp. As assessed by Southern 'Zoo-blot' analysis and direct cDNA sequence comparison, the human ribosomal protein L9 gene, like other ribosomal protein genes, is highly conserved among mammals.

Ultrastructural and biochemical analysis of sperm flagella from an infertile man with a rod-dominant retinal degeneration

This study examined the ultrastructural morphology and posttranslationally modified alpha-tubulin isoforms in the sperm flagella of a patient presenting with infertility and retinal degeneration. Clinical evaluation showed impaired motility and gross morphological abnormalities of the sperm and a rod-dominant retinal degeneration with midperipheral pigment clumping and scattered bone spicules. Other neurological indications included delayed neuroelectric transmission in the auditory brainstem and a temporal lobe seizure disorder. Ultrastructural analysis showed that 46% of sperm axonemes had missing and/or misplaced doublets compared with 10% to 12% in control subjects. ELISA analysis showed hypoacetylation of alpha-tubulin (30% of control) but normal levels of alpha-tubulin tyrosination. Tubulin acetyl-transferase specific activity was also 30% of control activity. These characteristics may be indicative of microtubule instability leading to the pathological consequences described.

Differential temporal and spatial expression of insulin-like growth factor binding protein-2 in developing chick ocular tissues

PURPOSE

To determine the developmental expression and localization of mRNA for insulin-like growth factor binding protein-2 (IGFBP-2), a major binding protein of IGF-I and IGF-II, in ocular tissues of the embryonic and early posthatched chick.

METHODS

In situ hybridization and northern blot analysis were used to analyze the cellular origin and relative expression of IGFBP-2 mRNA in ocular tissues.

RESULTS

Wholemount in situ hybridization reveals that, as early as 3.5 days of embryonic development (E3.5), IGFBP-2 mRNA is already expressed in many areas of the embryo, including surface ectoderm, certain regions of the brain, pharyngeal clefts, somites, and limb buds. In the eye, IGFBP-2 mRNA is expressed only in the presumptive corneal epithelium at this time. By E6, IGFBP-2 mRNA expression is present in both the corneal epithelium and endothelium. By E12, IGFBP-2 mRNA is detected clearly in the corneal stroma as well as in several other ocular structures, such as the sclera, eyelid, and ciliary body. In the neural retina, a low, diffuse expression of IGFBP-2 mRNA is found at E6, which becomes more localized to the nuclear layers by E12. Northern blot analysis confirms that a high level of IGFBP-2 expression is present in the cornea and sclera by E8 to E12. A high level of IGFBP-2 mRNA expression, however, is not observed in the retina until E18. At posthatch day 2 (P2), northern blot analyses of ocular tissues reveal that the cornea contains the highest ocular level of IGFBP-2 mRNA expression, a value equal to that of brain and liver.

CONCLUSIONS

The early appearance, along with differential temporal and spatial expression of IGFBP-2 mRNA in developing ocular tissues, suggests a role for IGFBP-2 in the regulation of growth and differentiation of several ocular tissues, including the cornea, sclera, and retina.

Identification of arylamine N-acetyltransferase activity in the bovine lens

Arylamine N-acetyltransferase (NAT) activity was identified and partially characterized in the bovine lens. According to size-exclusion HPLC, the molecular mass of the arylamine NAT is approximately 30-kDa. Based upon substrate specificity analysis, it is best described as an arylamine NAT which has some ability to N-acetylate arylalkylamines. This arylamine NAT acetylates para-aminobenzoic acid thereby demonstrating a monomorphic pattern of N-acetylation. It demonstrates low sensitivity to methotrexate inhibition as indicated by the relatively high IC50 value (470 microM). NAT could be involved in lenticular detoxification of both endogenous amines and exogenous drugs.

Soluble-binding proteins for docosahexaenoic acid are present in neural retina

PURPOSE

To determine if soluble binding proteins (BP) for fatty acids (FA), particularly docosahexaenoic acid (DHA), could be identified in the cytosol of rat and bovine retinas under in vitro and in vivo conditions.

METHODS

In vitro, cytosol fractions from normal bovine and rat retinas were delipidated and incubated with [14C]-DHA with or without a number of competing fatty acids. After crosslinking bound FA to BP, the proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and radioactivity determined in each fraction. For in vivo experiments, rats received [14C]-DHA by gavage. At selected periods after ingestion, retinas were collected and cytosolic fractions were prepared from each. These were crosslinked and subjected to SDS-PAGE, and radioactivity was determined in each fraction.

RESULTS

In vitro, several peaks of radioactivity (approximately 13, 20, 32, 43-45, 50, 63, and 94-105 kd) were found that exhibited [14C]-DHA binding. Relative specificity of binding was assessed by blocking of the [14C]-DHA binding with unlabeled DHA and by competition experiments with other FAs. After in vivo ingestion of [14C]-DHA, a large peak of radioactivity was observed at 43 kd by 4 hours. At 6 hours, this peak decreased and, after 24 hours, it approached baseline.

CONCLUSIONS

These findings demonstrate that there is a discrete grouping of proteins in retinal cytosol capable of binding DHA and other FA. Although the identities of these proteins have yet to be determined, the group may include a member of the 12- to 15-kd group of small fatty acid binding proteins (FABP). In particular, a unique 43-kd binding peak could play a major role in the uptake, binding, or both of DHA by the retina in vivo.

Isolation of candidate genes for macular degeneration using an improved solid-phase subtractive cloning technique

An improved solid-phase subtraction procedure was developed to generate a readily amplifiable library of short cDNA fragments highly enriched in the macula (target) versus the peripheral region (driver) of the monkey neural retina. The generated clones were sequenced and 63 were analyzed by northern blotting using total RNA from the monkey macula and peripheral retina. The results indicate that 32% are highly enriched in macula, 36% are below the limits of detection and 32% are not enriched. No clones were found which were enriched in the peripheral retina. Our technique is therefore successful in identifying novel cDNAs enriched in the macula area of the neural retina that may represent potential candidate genes for hereditary ocular diseases. It should thus be useful in other situations where subtle differences in expression between cell types or tissue areas need to be analyzed.

Cloning and characterization of a chick embryo cDNA and gene for IGF-binding protein-2

We have isolated and characterized a cDNA for IGF-binding protein-2 (IGFBP-2) and its gene from the chick embryo. Using primers from a conserved region of the mammalian IGFBP-2 sequence, a cDNA clone (1.6 kb) was isolated from an embryonic day-18 chick retina cDNA library. Although the clone was truncated at the 5' end, the complete coding sequence was obtained from 5' rapid amplification of cDNA ends and genomic sequencing. The open reading frame encoded a 311 amino acid precursor protein which contains a putative 36 residue signal peptide. The mature 275 amino acid protein had a predicted M(r) of 33,500 and exhibited 71, 68, 68 and 66% identity to rat, bovine, ovine and human IGFBP-2 cDNA respectively, with conservation of all 18 cysteines. The cDNA contained an RGD peptide but lacked a putative ATP-binding motif. A single transcript of approximately 2.3 kb was present in embryonic day-15 eye, brain, skeletal muscle, heart and intestine, but was virtually absent from embryonic day-15 liver. The chicken IGFBP-2 gene spanned approximately 38 kb, consisted of four exons, and was similarly organized to that of the rat and human. Southern blot analysis of chicken genomic DNA suggested that it is encoded by a single gene. The sequence information from the avian IGFBP-2 should be of value in examining the role of IGFBP-2 in vertebrate development.

Identification of pigment epithelium-derived factor in the interphotoreceptor matrix of bovine eyes

Pigment epithelium-derived factor (PEDF) is a neurotrophic protein and a member of the serine protease inhibitor superfamily. Here we describe the identification of PEDF in bovine eyes and optimization of its purification from this natural source. We have developed a polyclonal antibody to recombinant human PEDF, Ab-rPEDF, that immunoreacts in a specific, sensitive, and linear fashion with PEDF protein, and furthermore, blocks its neurotrophic activity. We show that Ab-rPEDF specifically recognizes a 49,500-M(r) polypeptide on Western transfers of a wash of the extracellular matrix between the retinal pigment epithelium and the neural retina-termed interphotoreceptor matrix (IPM). PEDF is present as approximately 1% of total soluble IPM protein. Starting with an IPM wash, PEDF protein is purified 164-fold to near homogeneity by ammonium sulfate fractionation and cation-exchange chromatography, with a recovery of 47%. The highly purified protein has an apparent M(r) of 49,500 +/- 1,500 as assessed by SDS-polyacrylamide gel electrophoresis, and a native pI of 7.0-7.7. It elutes as a single peak on gel-filtration chromatography with a retention time immediately behind that of ovalbumin (43,000 M(r)). N-glycosidase treatment indicates that each PEDF molecule has a 5% carbohydrate content attached to internal asparagine residue(s). Amino terminal sequence of the purified PEDF reveals removal of an amino-terminal peptide region for the mature protein. Purified PEDF has neurotrophic activity on human retinoblastoma cells, as previously observed for IPM. The neurotrophic activities of both PEDF and IPM are blocked by antiserum Ab-rPEDF. Altogether, PEDF is present in the bovine IPM as a soluble, extracellular, monomeric glycoprotein that by itself confers neurotrophic activity to the IPM. Thus, native PEDF isolated and purified as described here should prove useful for biochemical studies as well as other approaches.

Structural organization and expression of the human phosphatidylinositol-specific phospholipase C beta-3 gene

We have cloned and fully sequenced the phospholipase C beta-3 (PLC beta-3) gene. The gene spans approx. 17 kb and consists of 31 exons and 30 introns. All intron-exon junctions obey the GT/AG rule. The gene is highly expressed in several human tissues including retina, brain and kidney; PLC beta-3 mRNA is detected at a much lower level in liver. Because of its importance in signal transduction, its chromosomal localization and its high expression in CNS and other tissues, the PLC beta-3 gene is a candidate in several human genetic diseases which, with the present genomic sequence, can now be fully examined.

Vitreous and aqueous humors contain a latent proteinase activity that abolishes IGF binding to specific IGF binding proteins

Several distinct insulin-like growth factor binding proteins (IGFBPs) are present in tissues and fluids of the developing and adult eye. However, the mechanism(s) involved in the regulation of ocular IGFBP levels is unknown. We have now identified an endogenous factor in vitreous and aqueous humors that, when activated by sodium dodecyl sulfate (SDS), abolishes the capacity of specific low molecular weight IGFBPs (i.e. 24-30 kDa) to bind IGF as assessed by western ligand blotting. In contrast, IGF binding to the 46 and 32 kDa IGFBPs (IGFBP-3 and IGFBP-2 respectively) is not affected by the SDS-activated inhibitory factor (IF). Maximal activation of the IF occurs at an SDS concentration of approximately 0.015%. Incubations in the presence of the serine-proteinase inhibitor aprotinin result in marked inhibition of IF activity. Preliminary characterization by ultrafiltration suggests that the IF is large (< 100 kDa) and/or that it is present in a complex. The finding of a factor, most likely a serine proteinase, that specifically abolishes IGF binding to low molecular weight IGFBPs suggests a mechanism for regulating the levels of these IGFBPs and thus the functional activities of IGFs in ocular fluids under normal and/or pathological conditions.

Expression, secretion, and age-related downregulation of pigment epithelium-derived factor, a serpin with neurotrophic activity

Retinal pigment epithelial (RPE) cells form a functional complex with photoreceptor neurons of the retina, interacting through the interphotoreceptor matrix (IPM). We now provide evidence that the gene for pigment epithelium-derived factor (PEDF), a protein possessing neurotrophic and neuronal-survival activities, is highly expressed by both fetal and young adult RPE cells. PEDF mRNA is present in RPE cells of the human eye at 17 weeks of gestation, demonstrating its potential for action in vivo during early retinal development. The PEDF protein is secreted in vivo where it constitutes a part of the fetal and adult IPM surrounding photoreceptor outer segments. A polyclonal PEDF antibody recognizes at least four isoforms of secreted human and bovine PEDF by two dimensional gel analysis, and detects a similar 50 kDa protein in the IPM of several other vertebrate species. Within soluble extracts of RPE cells, however, where little, if any, of the 50 kDa species can be detected, an immunoreactive 36 kDa protein is observed by Western blot analysis. By immunofluorescence, PEDF is localized intracellularly in association with the nucleus, presumptive secretory granules, and cytoskeletal elements of cultured RPE cells with PEDF and actin antibodies colocalizing to the same cytoskeletal structures. During initial stages of attachment, PEDF and actin also concentrate at the tips of pseudopods extended by the cultured RPE cells. However, with successive passages, synthesis, and secretion of the PEDF protein as well as transcription of its mRNA decrease and are lost by about 10 passages. In parallel, cultured RPE cells lose their proliferative potential and change from an epithelial-like morphology in early passages to a more fibroblast-like appearance by about the 10th passage. PEDF is thus apparently present intracellularly and extracellularly in both fetal and early adult periods where it could be involved in cellular differentiation and survival and with its loss, in the onset of senescence.

Differences in arylalkylamine N-acetyltransferase activity between inflammatory disease-susceptible Lewis and -resistant Fischer rats

Lewis (LEW/N) and Fischer (F344/N) rats are histocompatible inbred strains characterized, respectively, by susceptibility and resistance to inflammatory disease. The susceptibility of LEW/N rats to inflammation has been associated with deficient corticotropin-releasing hormone (CRH), ACTH, and corticosterone responses to inflammatory stimuli, specifically attributed to a global impairment in hypothalamic CRH neuron function. In contrast to the LEW/N rats, F344/N rats demonstrate an intact hypothalamic-pituitary-adrenal (HPA) axis. Melatonin, a neurohormone initially isolated in the pineal gland, has been implicated with inhibition of the HPA axis. To investigate melatonin synthesis and secretion in LEW/N and F344/N rats, we examined the diurnal activity of pineal arylalkylamine N-acetyltransferase (NAT1), the rate-limiting enzyme in melatonin biosynthesis, which demonstrates circadian rhythmicity, as well as the diurnal levels of serum melatonin, in both strains. Arylamine N-acetyltransferase (NAT2), a related enzyme activity, thought not to be regulated in a circadian manner, was examined as a control of NAT1 activity. Pineal NAT1 activity peak was observed later and reached significantly higher levels in LEW/N than in F344/N rats. Serum melatonin levels reflected the circadian pattern of the NAT1 activity, without, however, showing any quantitative differences between the two strains. Time-course of pineal NAT1 activity response to beta-adrenergic stimulation was parallel in the two rat strains, whereas the magnitude of the response as greater in LEW/N than in F344/N rats. No circadian or major quantitative differences in NAT2 activity were found between the two strains. Size-exclusion HPLC chromatograms of NAT1 activity revealed similar patterns in both rat strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Pigment epithelium-derived factor is a survival factor for cerebellar granule cells in culture

Pigment epithelium-derived factor (PEDF), purified from human fetal retinal pigment epithelium cell culture medium, was shown to potentiate the differentiation of human Y-79 retinoblastoma cells. To investigate potential neurotrophic effects of PEDF on neurons other than those of retinal derivation, we used cultures of cerebellar granule cells. The number of cerebellar granule cells was significantly larger in the presence of PEDF, as demonstrated by an assay for viable cells that uses 3-(4,5-dimethylthiazol-2-yl)-5-(3- carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt, conversion, by cell count, and by immunocytochemistry. The effect of PEDF showed a dose-response relationship, with a larger effect in chemically defined medium than in serum-containing medium [ED50 = 30 ng/ml (0.70 nM) in chemically defined medium and 100 ng/ml (2.3 nM) in serum-containing medium]. PEDF had no effect on incorporation of bromodeoxyuridine (cell proliferation) or on neurofilament content (neurite outgrowth) measured by an enzyme-linked immunoadsorbent assay. These results demonstrate that PEDF has a neurotrophic survival effect on cerebellar granule cells in culture and suggest the possibility that it may affect other CNS neurons as well.

Induction of heme oxygenase 1 in the retina by intense visible light: suppression by the antioxidant dimethylthiourea

The effect of intense visible light (light damage) on the expression of heme oxygenase 1 (HO-1), a protein induced by oxidative stress, was investigated in the rat retina. A sensitive reverse transcription-PCR assay demonstrated the expression of mRNA for HO-1 as well as HO-2, the noninducible HO form, in the normal retina. As analyzed by Northern blotting, however, HO-1 mRNA was barely detectable under normal circumstances. After exposure to intense visible light, retinas had markedly higher HO-1 mRNA levels than unexposed controls, with increases up to 52- and 98-fold at 12 and 24 hr of exposure, respectively. Intense light exposure also resulted in an increase in HO-1 protein. In contrast, no appreciable change in HO-2 mRNA or protein was observed. The increase in HO-1 message was more pronounced in rats previously reared in the dark than in those reared in a weak cyclic-light environment. A marked decrease from the high level of HO-1 mRNA induced by light insult was observed when the animals were allowed to recover in the dark for 24 hr after light exposure. Most important, treatment of animals with 1,3-dimethylthiourea, a synthetic antioxidant, prior to light exposure effectively blocked the increase in HO-1 mRNA. Thus, HO-1 is a sensitive marker for assessing light-induced insult in the retina. Since increased expression of HO-1 is thought to be a cellular defense against oxidative damage, its expression may play an important role in protecting the retina against light damage.

Identification and partial characterization of a proteinase specific for insulin-like growth factor binding protein-3 in aqueous and vitreous humors

The IGFs (-I and -II) are normally found in serum and other extracellular fluids complexed to specific binding proteins (IGFBPs). While several IGFBPs have been identified in vitreous and aqueous humors, the major serum carrier of IGF, IGFBP-3, is notably absent from these fluids. To determine if this paucity could be due to an IGFBP-3 proteinase (IGFBP-3ase), samples of bovine vitreous or aqueous humor were mixed with serum and incubated at 37 degrees C for 4 h followed by western ligand blotting. In these experiments, a distinct loss of the 46 kDa band representing IGFBP-3 was observed while other bands present at 35, 28 and 25 kDa were unaltered. The IGFBP-3ase activity is temperature sensitive, has a pH optimum of about 8.0 and is inhibited by EDTA. Acid treatment of serum to remove endogenously bound IGF does not affect the specificity or activity of the IGFBP-3 proteinase. Size exclusion chromatography of bovine aqueous indicates an approximate molecular weight of 260 kDa. Incubation of recombinant IGFBP-3 or serum with partially-purified IGFBP-3ase results in the appearance of low molecular weight fragments of approximately 30 kDa. These fragments are undetectable by western ligand blotting but are readily visualized using an IGFBP-3 specific antibody. Comparison of normal and diabetic vitreous humor reveals the presence of an increased amount of IGFBP-3 proteolytic fragments in the diabetic as compared to control. These findings indicate the presence of a IGFBP-3 proteinase in aqueous and vitreous humors that may be important in regulating ocular homeostasis.

Neuron-specific enolase: a neuronal survival factor in the retinal extracellular matrix?

To identify soluble proteins of the retinal interphotoreceptor matrix (IPM), we isolated IPM from the bovine eye by gentle lavage and subjected it to SDS-PAGE. In the resultant gel, a 46 kDa band was particularly prominent and appeared to be a single protein. This protein was electroblotted to nitrocellulose membrane, digested with trypsin, and selected peptides were isolated by HPLC and subjected to Edman microsequencing. The amino acid sequences of the peptides were found to be virtually identical to that of human neuron-specific enolase (NSE). A monoclonal antibody specific for human NSE confirmed the presence of this enzyme in the bovine IPM by both Western blotting and immunocytochemical analysis. Immunofluorescence microscopy demonstrated that NSE is mainly localized to the basal domain of the IPM surrounding photoreceptor cells but is also prominent in the inner segments of the cone photoreceptor neurons. When NSE was added to cultures of human retinoblastoma cells, no effect on morphology was observed. However, a positive effect on cell growth and/or survival was readily apparent. It thus seems that not only is NSE a significant component of the retinal extracellular matrix, but that it could function as a survival (neuronotrophic) factor for photoreceptor neurons.

Structural analysis of the human hydroxyindole-O-methyltransferase gene. Presence of two distinct promoters

Hydroxyindole-O-methyltransferase (HIOMT) catalyzes the last step in the metabolic pathway that synthesizes the hormone melatonin. We have found HIOMT mRNA present in small amounts in human retina and in relatively high abundance in the pineal gland. Two distinct 5' ends were found in human retina using a solid-phase 5'-rapid amplification of cDNA ends technique. The two 5' regions appear to originate from two distinct putative promoters. Although many similarities exist between the two promoters, they contain distinctive elements. Putative promoter A, for example, contains a recently discovered photoreceptor-conserved element (PCE-1, CAATTAAG) at -27 not found in promoter B, while promoter B contains an Ap1 site (ATGAGTCAA) at -166 and an octamer site (ATGCAAT) at -59 not found in promoter A. The HIOMT messages are also alternatively spliced in between exons 6 and 8, generating three distinct messages. One of the alternatively spliced messages contains a line-1 repetitive element that is spliced into the mRNA precisely as exon 6. Importantly, the downstream open reading frame is not altered by any of these splicing combinations. The gene is approximately 35 kilobases long containing either 9 or 10 exons (including the line-1 element) depending on which promoter is active. All of the splice sites follow the GT/AG rule. The dual promoters and opportunities for alternative splicing suggest a variety of mechanisms for control of HIOMT expression and biological activity in different tissues not previously recognized.

An early decrease in interphotoreceptor retinoid-binding protein gene expression in Abyssinian cats homozygous for hereditary rod-cone degeneration

Levels of interphotoreceptor retinoid-binding protein (IRBP) protein and message in retinas of Abyssinian cats homozygous for progressive rod-cone degeneration were determined at early ages, well before the onset of clinical retinal degeneration. IRBP gene expression was assessed by immunochemical quantitation of IRBP protein, and by Northern blotting and slot-blotting of total RNA using a human IRBP cDNA probe. Morphology was assessed by electron microscopy and immunocytochemistry. Levels of both IRBP protein and message in affected Abyssinian cat retinas were significantly reduced below normal as early as 4 weeks of age at the earliest stage of retinal disorientation. Opsin mRNA was more abundant in affected Abyssinian cat retinas than in control retinas. This was at least 1 year before the onset of clinical symptoms. The reduction in IRBP gene expression to levels significantly below normal well before the onset of retinal degeneration in affected Abyssinian cat retinas indicates that this represents a primary defect or at least an early problem that could itself cause adverse effects.

Characterization of human B cell proteins binding specifically to uveitopathogenic peptide 1169-1191 of bovine IRBP

Peptide 1169-1191 is a major uveitopathogenic determinant of bovine Interphotoreceptor Retinoid Binding Protein (IRBP) in Lewis rats. Previously, we identified two proteins with approximate molecular masses of 72 and 74 kDa and one with a molecular mass of 40 kDa from B cells of naive Lewis rats and EBV-transformed B cells from a human patient with ocular Behçet's disease that bind to bovine IRBP peptide 1169-1191. In this study, we have partially characterized these proteins. The two proteins with molecular masses 72 and 74 kDa belong to the HSP 70 family of proteins and the 40-kDa protein is actin.

Retinoid processing in retinal pigment epithelium of toad (Bufo marinus)

The formation of 11-cis-[3H]retinal in the retinal pigment epithelium (RPE) and its release to extracellular medium containing interphotoreceptor retinoid-binding protein (IRBP) were studied in the RPE eyecup of the toad (Bufo marinus). The RPE was labeled with all-trans-[3H]retinol during an initial 1-h incubation. In phase 2 of the incubation (0-2 h), the extracellular medium contained initially ligand-free IRBP (0-26 microM). Retinoids subsequently extracted from the extracellular medium and RPE were analyzed by high performance liquid chromatography and scintillation counting. IRBP increased both the molar amount and specific radioactivity of 11-cis-retinal released by the RPE during phase 2. The molar amount of 11-cis-retinal in the RPE was small relative to that of retinal released with high IRBP. With 21 microM IRBP and phase 2 incubations of > or = 10 min, the specific radioactivity of released 11-cis-retinal exceeded that of all-trans-retinyl ester in the RPE. The specific radioactivity of 11-cis-retinyl ester was less than that of all-trans-ester, independent of IRBP concentration. The results indicate that IRBP promotes the formation (from all-trans-precursor) as well as the release of 11-cis-retinal and suggest the preferred utilization of recently incorporated and esterified all-trans-retinol in 11-cis-retinal synthesis in a "last in/first out" manner.

Characterization and novel activation of 72-kDa metalloproteinase in retinal interphotoreceptor matrix and Y-79 cell culture medium

Analysis of bovine interphotoreceptor matrix and conditioned medium from human Y-79 retinoblastoma cells by gelatin SDS-PAGE zymography reveals abundant activity of a 72-kDa M(r) gelatinase. The 72-kDa gelatinase from either source is inhibited by EDTA but not aprotinin or NEM, indicating that it is a metalloproteinase (MMP). The 72-kDa MMP is converted to a 62-kDa species with APMA treatment after gelatin sepharose affinity purification, typical of previously described gelatinase MMP-2. The latent 72-kDa gelatinase from either bovine IPM or Y-79 media autoactivates without APMA in the presence of calcium and zinc after 72 hr at 37 degrees C, producing a fully active mixture of proteinase species, 50 (48 in Y-79 medium), 38 and 35 kDa in size. The presence of inhibitory activity was examined in both whole bovine IPM and IPM fractions separated by SDS-PAGE. Whole IPM inhibited gelatinolytic activity of autoactivated Y-79-derived MMP in a dose-dependent manner. Inhibitory activities are observed in two protein fractions of 27-42 and 20-25 kDa. Western blots using antibodies to human tissue inhibitor of metalloproteinase 1 and 2 (TIMP-1 and -2) reveal the presence of two TIMP-1-like proteins at 21 and 29 kDa in inhibitory fractions of the bovine IPM. TIMP-2 was not detected in the inhibitory IPM fractions, consistent with the observed autoactivation of bovine IPM 72-kDa gelatinase. Potential roles for this IPM MMP-TIMP system include physiologic remodelling of the neural retina-RPE cell interface and digestion of shed rod outer segment as well as pathological processes such as retinal detachment, PE cell migration, neovascularization and tumor progression. Cultured Y-79 cells appear to be a good model for studying the production and regulation of this proteinase system.

Increased TRPM-2/clusterin mRNA levels during the time of retinal degeneration in mouse models of retinitis pigmentosa

Retinitis pigmentosa (RP) is a genetically and clinically heterogeneous group of human disorders that is characterized by diminished retinal function, visual cell loss, and blindness. Elevated levels of TRPM-2/clusterin mRNA, a marker for the apoptotic process, have been reported in retinas from patients with advanced stage RP. In the present study we examine TRPM-2/clusterin expression in two genetically distinct mouse models of RP, the rd (retinal degeneration) and rds (retinal degeneration slow) mice. We establish that in advanced postretinal degenerative stages of the rd mutant the retinal TRPM-2/clusterin mRNA levels are highly elevated, as is seen in the case of human RP. Examination of TRPM-2/clusterin mRNA levels in retina and whole eyes from the rd mouse and morphologically normal controls during the period of retinal degeneration (postnatal days 8-21) in the rd phenotype shows that TRPM-2/clusterin mRNA levels are elevated in the rd animal, and this increase begins just after postnatal day 10 and remains high for the remainder of the time course examined. Northern analysis of rds retina and whole eyes shows a delayed increase in TRPM-2/clusterin mRNA levels relative to the rd profile, coinciding with the known period of rds retinal degeneration (postnatal day 14 to 1 year). In each case, the onset of increased TRPM-2/clusterin mRNA levels coincides with the time of photoreceptor cell death.

A glycoprotein binding retinoids and fatty acids is present in Drosophila

In the search for a possible Drosophila melanogaster homolog of interphotoreceptor retinoid-binding protein (IRBP), a approximately 140-kDa retinoid- and fatty acid-binding glycoprotein found in vertebrates, the 110,000 g supernatant fraction prepared from homogenates of fly heads was analyzed for the presence of proteins capable of binding radiolabeled retinol and palmitic acid. A soluble protein, which binds concanavalin A and has a retention time on size-exclusion high-performance liquid chromatography identical to that of purified bovine IRBP, was identified as binding both ligands. As assessed by fluorescence titration, the protein fraction obtained by concanavalin A-Sepharose affinity chromatography and size-exclusion chromatography of fly head supernatant had apparent dissociation constants of 2.9 x 10(-7) +/- 0.6 M for all-trans retinol, with the number (n) of independent ligand binding sites per protein molecule = 2, and 3.5 x 10(-7) +/- 0.1 M for 16-[9-anthroyloxy] palmitic acid with n = 7. High-performance liquid chromatography of hexane extracts of this protein fraction resolved several peaks with polarity and relative retention times similar, but not identical to all-trans retinol and retinal and their 9-, 11-, and 13-cis isomers. Gas chromatography/mass spectrometry analysis of fatty acid methyl esters prepared following lipid extraction of the protein identified lauric, myristic, palmitic, palmitoleic, and oleic acids as being covalently bound. Laurate, myristate, palmitate, and stearate were noncovalently bound. The apparent molecular mass of the Drosophila protein as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining of the retinoid- and fatty acid-binding peak obtained by hydrophobic interaction chromatography of the size-exclusion fraction was approximately 70 kDa.

Heme oxygenase-1 is associated with the neurofibrillary pathology of Alzheimer's disease

Heme oxygenase-1 is an important enzyme that degrades heme, a pro-oxidant, leading to the formation of antioxidant molecules. In this study we demonstrate by immunocytochemistry close association of heme oxygenase-1 with Alzheimer neurofibrillary pathology and with the neurofibrillary tangles found in progressive supranuclear palsy and subacute sclerosing panencephalitis. In Alzheimer's disease, using two different rabbit antisera against heme oxygenase-1 protein, we localized, using immunocytochemical methods, heme oxygenase-1 to neurofibrillary tangles, senile plaque neurites, granulovacuolar degeneration, and neuropil threads. Only light background staining was seen in young controls and sporadic lesion-related immunoreactivity in age-matched controls. The increase in heme oxygenase-1 protein in association with the neurofibrillary pathology of Alzheimer's disease and other diseases characterized by neurofibrillary tangles supports the notion that the generation of free radicals and oxidative stress plays a role in the pathogenesis of neurofibrillary pathology.

Vitreal insulin-like growth factor binding proteins (IGFBPs) are increased in human and animal diabetics

Although patients with diabetic retinopathy have been reported to have elevated vitreal IGF-I levels, it is not known whether diabetes also affects the levels of vitreal IGF binding proteins (IGFBPs) which control IGF's bioavailability. To address this issue, vitreal IGFBP levels were assayed in human diabetics, rats with streptozotocin-induced diabetes and galactose-fed dogs with diabetic-like retinopathy. Using 125I-IGF-II ligand blots, it was found that human diabetics have a 4-fold increase in vitreal IGFBP levels. Also, western blots on human diabetic vitreous reveal increased levels of IGFBP-2 and proteolytic fragments of IGFBP-3. IGF binding assays on vitreous from streptozotocin-treated rats (three months in duration) also indicate a 5-fold increase in IGF binding activity. IGF ligand blots using vitreous from rats with a shorter duration of diabetes (one month) show a 63% increase in IGFBP binding and a marked decrease in serum IGFBP binding. IGF ligand blots and IGFBP-2 and -4 western blots using vitreous from galactose-fed dogs with diabetic-like retinopathy exhibit a 6-fold increase in vitreal IGFBPs. The observation that vitreal IGFBPs are elevated in diabetic humans and rats without overt retinopathy suggests that these increases are not the result of a preexisting end-stage retinopathy but rather are an early ocular event in the diabetic process. Increases in vitreal IGFBPs thus could participate in the proliferative aspects of diabetic retinopathy by virtue of their putative intrinsic bioactivity or their capacity to alter IGF bioavailability.

Increased expression of heme oxygenase-1 in human retinal pigment epithelial cells by transforming growth factor-beta

Antibodies specific for heme oxygenase-1 (HO-1) were produced in rabbits, using the multiple antigen peptide (MAP) technique, and were employed to investigate the ability of transforming growth factor-beta 1 (TGF-beta 1) to induce the HO-1 protein in cultured human retinal pigment epithelial (RPE) cells. Western blot analyses showed that the cytokine induced HO-1 in these cells in a time- and dose-dependent manner. TGF-beta 1 also increased the mRNA for HO-1 in treated cells prior to the increase in HO-1 protein. The induction was effectively blocked by a neutralizing antibody preparation against TGF-beta 1. When tested under similar conditions, other growth factors such as basic fibroblast growth factor-I, platelet-derived growth factor, insulin-like growth factor, transforming growth factor-alpha, and epidermal growth factor did not show appreciable induction of HO-1. Lipopolysaccharide, tumor necrosis factor-alpha, and interferon-gamma were also not inducers, although TGF-beta 2 effectively induced HO-1. Heavy metal ions and thiol reagents were also highly potent inducers of HO-1 in human RPE cells. The induction of HO-1 by TGF-beta 1 was also observed in bovine choroid fibroblasts, but not in HELA, HEL or bovine corneal fibroblasts. Our results demonstrate for the first time that HO-1 can be induced by an important cytokine, TGF-beta 1, causing an increase in the expression of both HO-1 message and protein in specific neuroepithelial and fibroblast cells.

Chromosomal localization of the human heme oxygenase genes: heme oxygenase-1 (HMOX1) maps to chromosome 22q12 and heme oxygenase-2 (HMOX2) maps to chromosome 16p13.3

Heme oxygenase catalyzes the oxidation of heme to biliverdin, the precursor of the bile pigment bilirubin, and carbon monoxide, a putative neurotransmitter. We have employed polymerase chain reaction and fluorescence in situ hybridization to determine the chromosome localization of the genes coding for the two known heme oxygenase isozymes. Heme oxygenase-1 (HMOX1), the inducible form, was localized to human chromosome 22q12, while heme oxygenase-2 (HMOX2), the constitutive form, was localized to chromosome 16p13.3.

Identification of heat shock proteins binding to an immunodominant uveitopathogenic peptide of IRBP

Intracellular binding proteins have been identified and isolated from B cells by their ability to bind to the synthetic peptide (1169-1191), the major immunodominant epitope of bovine interphotoreceptor retinoid-binding protein (IRBP) coupled to cyanogen bromide activated Sepharose 4B. After SDS-PAGE, two discrete protein bands of approximately 72 and 74 kDa, were found to be present in B cells of naive Lewis rats as well as in EBV transformed B cells from a human patient with ocular Behçet's disease. Enhanced expression of these peptide-binding proteins was achieved by incubating the cells with Lipopolysaccharide (LPS) from S. typhimurium. The approximately 72 and 74 kDa peptide-binding proteins reacted in western blot with monoclonal antibodies specific for both constitutively expressed and inducible 72/74 kDa hsp 70 proteins. The demonstration that these proteins bind to the immunodominant epitope of IRBP indicates that they may play a role in the processing and presentation of antigens by antigen-presenting cell (APC).

Localization of the gene for pigment epithelium-derived factor (PEDF) to chromosome 17p13.1 and expression in cultured human retinoblastoma cells

The gene for pigment epithelium-derived factor (PEDF) was localized to chromosome 17 by the analysis of three independent somatic cell hybrid panels. Fluorescence in situ hybridization shows a specific hybridization signal at the terminal portion of the short arm of chromosome 17. PCR analysis of somatic cell hybrids containing specific regions of 17 was subsequently used to sublocalize PEDF to 17p13.1-pter. PEDF thus maps to a region containing a number of cancer-related loci and thus must be considered a candidate gene for these cancers. Preliminary studies with cultured human Y79 retinoblastoma cells indicate that expression of PEDF is associated with relatively undifferentiated, proliferating cells rather than their differentiated, slow-growing counterparts. This and the fact that the PEDF protein can act as a potent neurotrophic differentiating agent suggest that PEDF is linked to proliferative events that terminate in final phenotypic determination within specific cell lineages.

Assay of tubulin acetyltransferase activity in subcellular tissue fractions

An assay for alpha-tubulin acetyltransferase (TAT) activity based on affinity isolation of labeled acetylated alpha-tubulin was developed for use with crude subcellular fractions. Microtubules were polymerized and immobilized on an anti-alpha-tubulin-agarose and then incubated with the subcellular fraction and [3H]acetyl-coenzyme A (CoA). The labeled product was eluted from the antibody-agarose and the tritiated acetate incorporation determined. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot of the eluate verified the presence of acetyl-alpha-tubulin. Analysis of bovine retinal fractions showed the highest specific activity of tubulin acetyltransferase activity in the 27,000g pellet fraction (P2) of retinal homogenates. This transferase activity was proportional to the concentration of microtubule protein immobilized under polymerizing conditions and had an apparent Km of 3 microM for acetyl-CoA. The activity was solubilized from the P2 pellet by a high ionic strength buffer. The properties of the retinal TAT determined by this assay are very similar to those reported for a more purified enzyme preparation from Chlamydomonas flagella using the conventional trichloroacetic acid precipitation assay and support the use of this method for samples in which high backgrounds prohibit use of the conventional assay.

Light deprivation profoundly affects gene expression of interphotoreceptor retinoid-binding protein in the mouse eye

Ambient light appears to play a role in regulating gene and protein expression of interphotoreceptor retinoid-binding protein (IRBP), a protein that facilitates the transport of retinoids between the neural retina and pigment epithelium in the visual cycle. Pregnant CD-1 mice were placed in the dark approximately 48 hr before parturition, and the pups were reared for 14 days under these conditions. Control animals were reared on a 12 hr light/12 hr dark cycle. Northern blotting of total RNA isolated from whole mouse eyes at post-natal days 7-14 (P7-P14) showed a marked reduction in IRBP message in the light-deprived animals to 10-20% of levels in control animals. Reprobing of the blots for opsin and S-antigen message showed a significant decrease of about 80-90% in opsin message at 5.1 kb but no change in S-antigen message in the eyes of light-deprived mice. Light microscopic examination of the light-deprived mouse retinas showed no apparent abnormalities in morphological development and immunocytochemistry demonstrated normal distribution and levels of IRBP protein. Immunochemical quantitation of IRBP protein confirmed that there was no reduction in light-deprived as compared to normal mouse eyes. Similarly, when adult mice were light-deprived for 14 days, a marked reduction in IRBP message was also observed with no decrease in the amount of IRBP protein. Thus, light deprivation causes a large decrease in IRBP message in the mouse eye, but IRBP protein is not decreased. The dramatic effect of light deprivation on IRBP mRNA and some opsin mRNAs, but not on S-antigen message and the fact that IRBP protein levels are relatively unaffected, suggest a complex pathway of light regulation of photoreceptor function previously not encountered. This may involve regulatory controls at levels including gene transcription, mRNA stability or protein degradation that may make use of a feedback control mechanism involving light- or dark-dependent signal transduction.